Process for the manufacture of hydrated oxides and tri- and tetra- basic lead sulphates

ABSTRACT

Process for the manufacture of hydrated lead oxides in the bivalent state characterized by the step of (1) reacting metallic lead with acetic acid (e.g. ammonium acetate, 5%-30% solution) at a temperature up to 200° C. (e.g. 50°-200° C.) under an atmosphere of an oxygen containing gas (e.g. oxygen) of between 1 and 10 atmospheres absolute pressure to form lead acetate, then (2) reacting the lead acetate with a source of ammonium ion (e.g. ammonia) under an absolute pressure between 1 and 5 atmospheres at a temperature up to 100° C. (e.g. 60°-90° C.) to precipitate lead oxides and, optionally, to produce tri- and tetra- basic lead sulphates, by (3) adding to the lead oxides so precipitated sulphuric acid in the stoichliometric amount to produce tri- or tetra- basic lead sulphate, then (4) separating and drying the tri- or tetra- basic lead sulphate so formed.

TECHNICAL FIELD

This invention relates to the manufacture of hydrated lead oxides in thebivalent state which may be used commercially as the starting point inthe making of all lead chemicals.

More particularly these hydrated lead oxides are useful in the plasticindustry to produce stabilizers for polyvinyl chloride resins againstthermal and ultraviolet degradation. Typical derivatives are tri-basiclead sulphate, tetra-basic lead silico sulphate, lead silicon sulphate,dibasic lead phosphite, lead phthalate, dibasic lead stearate and leadstearate.

The hydrated lead oxides are also useful in the paint and pigmentindustry.

BACKGROUND ART

The stabilizers aforementioned are presently manufactured by a processwhich involves the production of litharge by blowing air through moltenlead at very high temperatures. The litharge so produced is slurriedwith water and then with sulphuric acid under controlled conditions tocause the tri-basic lead sulphate to precipitate. This precipitate isseparated and dried ready for use as a stabilizer. It is found that thisprocess causes a high degree of atmospheric pollution, and that thefinal product contains an undesirably high concentration of unreactedlead. For instance in U.S. Pat. No. 3,323,859 dibasic lead saltstabilizers for PVC are manufactured by reacting litharge with diluteacetic acid, and the dibasic lead acetate so formed is reacted withsodium sulphate.

Various approaches have been taken to avoid the use of litharge in theproduction of stabilizers. In U.S. Pat. No. 452,386, metallic lead isconverted to lead acetate by subjecting it to the alternate action ofdilute acetic acid and of atmospheric air, then reacting the leadacetate with sulphuric acid.

DISCLOSURE OF THE INVENTION

It is the principal object of the present invention to provide a processfor the manufacture of hydrated lead oxides in the bivalent state, whichminimizes pollution and yields a product which may be utilized in thepaints and pigment industries and also to avoid the use of litharge inthe production of PVC stabilizers.

Accordingly there is provided a process for the manufacture of hydratedlead oxides in the bivalent state characterized by the steps of (1)reacting metallic lead with acetic acid at a temperature up to 200° C.under an atmosphere of an oxygen containing gas of between 1 and 10atmospheres absolute pressure to form lead acetate, then (2) reactingthe lead acetate with a source of ammonium ion under an absolutepressure between 1 and 5 atmospheres up to 100° C. to precipitatehydrated lead oxides.

The acetic acid may be present in concentrations of up to 50% wt.,preferably up to 25% wt. and if added as ammonium acetate concentrationsof up to 50% wt., preferably 35% wt. should be used.

In a preferred embodiment of the invention the process may include theadditional step of adding sulphuric acid and/or ammonium sulphate to thehydrated lead oxides to produce tri- or tetra-basic lead sulphate.Additionally the tri- or tetra-basic lead sulphate can be separated anddried.

In a particularly preferred form of the invention is a process for themanufacture of tri- and tetra-basic lead sulphates, characterized by thesteps of (1) reacting excess metallic lead with an aqueous solutioncontaining between 5% and 30% by weight of ammonium acetate at atemperature between 50° C. and 200° C. under an atmosphere of oxygen ofbetween 1 and 10 atmospheres absolute pressure to form lead acetate,then (2) reacting the lead acetate so formed with ammonia under anabsolute pressure between 1 and 5 atmospheres at a temperature between15° C. and 100° C., preferably 60° C. to 90° C., to precipitate leadoxides, then (3) adding to the lead oxides so precipitated sulphuricacid in the stoichiometric amount to produce tri- or tetra-basic leadsulphate, then (4) separating and drying the tri- or tetra-basic leadsulphate so formed.

Preferably in step (1) the concentration of the aqueous solution ofammonium acetate is between 15% and 25% by weight, the temperature isbetween 80° C. and 120° C., and the pressure is between 3 and 5atmospheres absolute.

In a most preferred form of step (1) the concentration of the aqueoussolution of ammonium acetate is 20% by weight, the temperature is 100°C., and the pressure is 2.5 atmospheres absolute, and in step (2) thetemperature is 80° C. and the pressure is 3 atmospheres absolute.

The following examples disclose two forms of the invention and theaccompanying single sheet of drawing is a flow chart whichdiagrammatically illustrates the procedures followed:

EXAMPLE 1

An aqueous solution of ammonium acetate at a concentration of 35% byweight and a temperature of 100° C. was reacted for 1 hour with excessmetallic lead in a closed reactor through which oxygen was passed. Theammonium acetate dissociates and the acetic acid formed reacted with thelead under an atmosphere of oxygen at 5 atmospheres absolute pressure toproduce a lead acetate solution and ammonia. The ammonia was carriedaway and condensed and the oxygen stream was returned to the reactor.

The temperature of the aqueous solution of lead acetate was adjusted to80° C., and it was transferred to a precipitator, into which ammoniaincluding that recovered from the previous stage was directed until apressure of 3 atmospheres absolute was achieved. Hydrated lead oxideswere precipitated, and ammonium acetate solution was formed.

EXAMPLE 2

The same procedure as disclosed in Example 1 was followed.

Sulphuric acid in the stoichiometric amount reacted with the hydratedlead oxides of Example 1 in the precipitator thereby converting thehydrated lead oxides into tri-basic lead sulphate, which formed aprecipitate. This precipitate was separated from the liquid in which itwas dispersed, and dried. Starting with 83.6 kg. of lead, a yield of 100kg. of dry tri-basic lead sulphate was obtained.

The resulting solid was incorporated as a stabilizer in polyvinylchloride resin, which was then passed through an extruder to form testpieces. The liquid was heated in a stripping circuit to drive off anydissolved ammonia, which was recovered for re-use and to adjust theconcentration of ammonium acetate to 35% by weight. It was then directedto the reactor for the first stage of a repetition of the process on afresh batch of metallic lead.

On comparison with similar pieces made from the same resin withcommercially available stabilizers, the test pieces provided by theprocess according to the present invention were found to be moreeffectively stabilized without sacrifice of any desirable properties ofthe resin. Furthermore, the tribasic lead sulphate resulting from theprocess according to the present invention was substantially free (lessthan 5 ppm) of elemental lead, mono basic lead sulphate and unreactedlead oxides.

It will be observed that the method according to the present inventionoperates at moderate temperatures and pressures, so that the capitalcost of the apparatus required is considerably less than that requiredfor the conventional process, and the operating costs are also lower.

I claim:
 1. A process for the manufacture of hydrated lead oxides in the bivalent state characterized by the steps of (1) reacting metallic lead with acetic acid at a temperature up to 200° C. under an atmosphere of an oxygen containing gas of between 1 and 10 atmospheres absolute pressure to form lead acetate, then (2) reacting the lead acetate with a source of ammonium ion under an absolute pressure between 1 and 5 atmospheres at a temperature up to 100° C. to precipitate hydrated lead oxides.
 2. A process according to claim 1 wherein the concentration of acetic acid is up to 50% wt., preferably up to 25% wt.
 3. A process according to claim 1 wherein the acetic acid is added in the form of an aqueous solution containing ammonium acetate.
 4. A process according to claim 3 wherein the concentration of ammonium acetate in the aqueous solution is up to 50% wt., preferably up to 35% wt.
 5. A process according to claim 1 comprising the additional step of adding sulphuric acid and/or ammonium sulphate to the hydrated lead oxides to produce tri- or tetra-basic lead sulphate.
 6. A process according to claim 5 comprising the additional step of separating and drying the tri- or tetra-basic lead sulphate.
 7. A process for the manufacture of tri- and tetra-basic lead sulphates, characterized by the steps of (1) reacting excess metallic lead with an aqueous solution containing between 5% and 30% by weight of ammonium acetate at a temperature between 50° C. and 200° C. under an atmosphere of oxygen of between 1 and 10 atmospheres absolute pressure to form lead acetate, then (2) reacting the lead acetate so formed with ammonia under an absolute pressure between 1 and 5 atmospheres at a temperature between 15° C. and 100° C., preferably 60° C. to 90° C. to precipitate lead oxides, the (3) adding to the lead oxides so precipitated sulphuric acid in the stoichiometric amount to produce tri- or tetra-basic lead sulphate, then (4) separating and drying the tri- or tetra-basic lead sulphate so formed.
 8. A process according to claim 7, characterized in that in step (1) the concentration of the aqueous solution of ammonium acetate is between 15% and 25% by weight, the temperature is between 80° C. and 120° C., and the pressure is between 3 and 5 atmospheres absolute.
 9. A process according to claim 7 or 8, characterized in that step (2) is conducted at a temperature between 60° C. and 90° C.
 10. A process according to claim 7, characterized in that in step (1) the concentration of the aqueous solution of ammonium acetate is 20% by weight, the temperature is 100° C., and the pressure is 2.5 atmospheres absolute, and in that in step (2) the temperature is 80° C. and the pressure is 3 atmospheres absolute. 